They're counting on the 10th Amendment which gives any power not specifically granted to the Federal Government to the States and vice versa. But, if the Federal Government suddenly makes a law that directly impacts the States, the States have to suck it up and go with it. They can challenge, which they're certainly doing right now, but in the end, Federal Courts will side with the Federal Government especially with laws that have long standing.
Ironbite-also the Federal Government can choose what to do with any State law...such as certain state drug laws that have been passed recently.